/* Aseprite (.ase) file parser
 *
 * DEFLATE decoder based on Handmade Hero's png parser
 */

////////////////////////////////
//~ Shared constants

Global Readonly u32 ASE_huff_hclen_order[] = {
    16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15
};

Global Readonly ASE_HuffEntry ASE_huff_length_table[] = {
    {3, 0},     /* 257 */
    {4, 0},     /* 258 */
    {5, 0},     /* 259 */
    {6, 0},     /* 260 */
    {7, 0},     /* 261 */
    {8, 0},     /* 262 */
    {9, 0},     /* 263 */
    {10, 0},    /* 264 */
    {11, 1},    /* 265 */
    {13, 1},    /* 266 */
    {15, 1},    /* 267 */
    {17, 1},    /* 268 */
    {19, 2},    /* 269 */
    {23, 2},    /* 270 */
    {27, 2},    /* 271 */
    {31, 2},    /* 272 */
    {35, 3},    /* 273 */
    {43, 3},    /* 274 */
    {51, 3},    /* 275 */
    {59, 3},    /* 276 */
    {67, 4},    /* 277 */
    {83, 4},    /* 278 */
    {99, 4},    /* 279 */
    {115, 4},   /* 280 */
    {131, 5},   /* 281 */
    {163, 5},   /* 282 */
    {195, 5},   /* 283 */
    {227, 5},   /* 284 */
    {258, 0},   /* 285 */
};

Global Readonly ASE_HuffEntry ASE_huff_dist_table[] = {
    {1, 0},         /* 0 */
    {2, 0},         /* 1 */
    {3, 0},         /* 2 */
    {4, 0},         /* 3 */
    {5, 1},         /* 4 */
    {7, 1},         /* 5 */
    {9, 2},         /* 6 */
    {13, 2},        /* 7 */
    {17, 3},        /* 8 */
    {25, 3},        /* 9 */
    {33, 4},        /* 10 */
    {49, 4},        /* 11 */
    {65, 5},        /* 12 */
    {97, 5},        /* 13 */
    {129, 6},       /* 14 */
    {193, 6},       /* 15 */
    {257, 7},       /* 16 */
    {385, 7},       /* 17 */
    {513, 8},       /* 18 */
    {769, 8},       /* 19 */
    {1025, 9},      /* 20 */
    {1537, 9},      /* 21 */
    {2049, 10},     /* 22 */
    {3073, 10},     /* 23 */
    {4097, 11},     /* 24 */
    {6145, 11},     /* 25 */
    {8193, 12},     /* 26 */
    {12289, 12},    /* 27 */
    {16385, 13},    /* 28 */
    {24577, 13},    /* 29 */
};

Global Readonly u32 ASE_huff_bl_counts[][2] = {
    {143, 8},
    {255, 9},
    {279, 7},
    {287, 8},
    {319, 5},
};

////////////////////////////////
//~ Ase bitbuff

u32 ASE_PeekBits(ASE_Bitbuff *bb, u32 nbits)
{
    Assert(nbits <= 32);

    u64 cur_byte = bb->cur_bit >> 3;
    u8 bit_index = bb->cur_bit % 8;
    u64 nbytes = (nbits + bit_index + 7) >> 3;

    u64 val64 = 0;
    CopyBytes(&val64, &bb->data[cur_byte], nbytes);
    u32 val32 = (u32)(val64 >> bit_index);
    val32 &= U32Max >> (32 - nbits);

    return val32;
}

u32 ASE_ConsumeBits(ASE_Bitbuff *bb, u32 nbits)
{
    u32 val = ASE_PeekBits(bb, nbits);
    bb->cur_bit += nbits;
    return val;
}

void ASE_SkipBits(ASE_Bitbuff *bb, u32 nbits)
{
    bb->cur_bit += nbits;
}

////////////////////////////////
//~ Inflate

u32 ASE_ReverseBits(u32 v, u32 bit_count)
{
    /* 7 & 15 seem to be the most common bit_counts, so a
     * more optimal path is layed out for them. */
    if (bit_count == 15)
    {
        u32 b1 = v & 0xFF;
        b1 = (b1 & 0xF0) >> 4 | (b1 & 0x0F) << 4;
        b1 = (b1 & 0xCC) >> 2 | (b1 & 0x33) << 2;
        b1 = (b1 & 0xAA) >> 1 | (b1 & 0x55) << 1;

        u32 b2 = (v & 0xFF00) >> 8;
        b2 = (b2 & 0xF0) >> 4 | (b2 & 0x0F) << 4;
        b2 = (b2 & 0xCC) >> 2 | (b2 & 0x33) << 2;
        b2 = (b2 & 0xAA) >> 1 | (b2 & 0x55) << 1;
        b2 >>= 1;

        return (b1 << 7) | b2;
    }
    else if (bit_count == 7)
    {
        v = (v & 0xF0) >> 4 | (v & 0x0F) << 4;
        v = (v & 0xCC) >> 2 | (v & 0x33) << 2;
        v = (v & 0xAA) >> 1 | (v & 0x55) << 1;
        return v >> 1;

    }
    else
    {
        u32 result = 0;
        for (u32 i = 0; i <= (bit_count / 2); ++i)
        {
            u32 inv = (bit_count - (i + 1));
            result |= ((v >> i) & 0x1) << inv;
            result |= ((v >> inv) & 0x1) << i;
        }
        return result;
    }
}

ASE_HuffDict ASE_InitHuffDict(Arena *arena, u32 max_code_bits, u32 *bl_counts, u32 bl_counts_count)
{
    __prof;

    ASE_HuffDict result = ZI;
    result.max_code_bits = max_code_bits;
    result.entries_count = (1 << max_code_bits);
    result.entries = PushStructsNoZero(arena, ASE_HuffEntry, result.entries_count);

    u32 code_length_hist[ASE_HuffBitCount] = ZI;
    for (u32 i = 0; i < bl_counts_count; ++i)
    {
        u32 count = bl_counts[i];
        Assert(count <= countof(code_length_hist));
        ++code_length_hist[count];
    }

    u32 next_code[ASE_HuffBitCount] = ZI;
    next_code[0] = 0;
    code_length_hist[0] = 0;
    for (u32 i = 1; i < countof(next_code); ++i)
    {
        next_code[i] = ((next_code[i - 1] + code_length_hist[i - 1]) << 1);
    }

    for (u32 i = 0; i < bl_counts_count; ++i)
    {
        u32 code_bits = bl_counts[i];
        if (code_bits)
        {
            Assert(code_bits < countof(next_code));
            u32 code = next_code[code_bits]++;
            u32 arbitrary_bits = result.max_code_bits - code_bits;
            u32 entry_count = (1 << arbitrary_bits);
            for (u32 entry_index = 0; entry_index < entry_count; ++entry_index)
            {
                /* TODO: Optimize this. It's bloating up the loading times. */
                u32 base_index = (code << arbitrary_bits) | entry_index;
                u32 index = ASE_ReverseBits(base_index, result.max_code_bits);
                ASE_HuffEntry *entry = &result.entries[index];
                entry->symbol = (u16)i;
                entry->bits_used = (u16)code_bits;
            }
        }
    }

    return result;
}

u16 ASE_DecodeHuffDict(ASE_HuffDict *huffman, ASE_Bitbuff *bb)
{
    u32 index = ASE_PeekBits(bb, huffman->max_code_bits);
    Assert(index < huffman->entries_count);

    ASE_HuffEntry *entry = &huffman->entries[index];
    u16 result = entry->symbol;
    ASE_SkipBits(bb, entry->bits_used);
    Assert(entry->bits_used > 0);
    return result;
}

void ASE_Inflate(u8 *dst, u8 *encoded)
{
    TempArena scratch = BeginScratchNoConflict();

    __prof;
    ASE_Bitbuff bb = { .data = encoded };

    /* ZLIB header */
    u32 cm = ASE_ConsumeBits(&bb, 4);
    u32 cinfo = ASE_ConsumeBits(&bb, 4);
    Assert(cm == 8);
    Assert(cinfo == 7);

    u32 fcheck = ASE_ConsumeBits(&bb, 5);
    u32 fdict = ASE_ConsumeBits(&bb, 1);
    u32 flevl = ASE_ConsumeBits(&bb, 2);
    Assert(fdict == 0);

    u8 cmf = (u8)(cm | (cinfo << 4));
    u8 flg = fcheck | (fdict << 5) | (flevl << 6);
    (UNUSED)cmf;
    (UNUSED)flg;
    Assert(((cmf * 256) + flg) % 31 == 0);

    u8 bfinal = 0;
    while (!bfinal)
    {
        bfinal = ASE_ConsumeBits(&bb, 1);
        u8 btype = ASE_ConsumeBits(&bb, 2);
        switch (btype)
        {
            case ASE_BlockType_Uncompressed:
            {
                ASE_SkipBits(&bb, (8 - (bb.cur_bit % 8)) % 8);
                i16 len = ASE_ConsumeBits(&bb, 16);
                i16 nlen = ASE_ConsumeBits(&bb, 16);
                Assert(len == ~nlen);  /* Validation */
                (UNUSED)nlen;
                while (len-- > 0)
                {
                    *dst++ = ASE_ConsumeBits(&bb, 8);
                }
            } break;

            case ASE_BlockType_CompressedFixed:
            case ASE_BlockType_CompressedDynamic:
            {
                TempArena temp = BeginTempArena(scratch.arena);
                u32 lit_len_dist_table[512] = ZI;
                u32 hlit;
                u32 hdist;

                if (btype == ASE_BlockType_CompressedDynamic)
                {
                    /* Dynamic table */

                    /* Read huffman table */
                    hlit = ASE_ConsumeBits(&bb, 5) + 257;
                    hdist = ASE_ConsumeBits(&bb, 5) + 1;
                    u32 hclen = ASE_ConsumeBits(&bb, 4) + 4;

                    /* Init dict huffman (hclen) */
                    u32 hclen_bl_counts[19] = ZI;
                    for (u32 i = 0; i < hclen; ++i)
                    {
                        u32 code = ASE_huff_hclen_order[i];
                        hclen_bl_counts[code] = ASE_ConsumeBits(&bb, 3);
                    }
                    ASE_HuffDict dict_huffman = ASE_InitHuffDict(temp.arena, 7, hclen_bl_counts, countof(hclen_bl_counts));

                    /* Decode dict huffman */
                    u32 lit_len_count = 0;
                    u32 len_count = hlit + hdist;
                    Assert(len_count <= countof(lit_len_dist_table));
                    while (lit_len_count < len_count)
                    {
                        u32 rep_count = 1;
                        u32 rep_val = 0;
                        u32 encoded_len = ASE_DecodeHuffDict(&dict_huffman, &bb);
                        if (encoded_len <= 15)
                        {
                            rep_val = encoded_len;
                        }
                        else if (encoded_len == 16)
                        {
                            rep_count = 3 + ASE_ConsumeBits(&bb, 2);
                            Assert(lit_len_count > 0);
                            rep_val = lit_len_dist_table[lit_len_count - 1];
                        }
                        else if (encoded_len == 17)
                        {
                            rep_count = 3 + ASE_ConsumeBits(&bb, 3);
                        }
                        else if (encoded_len == 18)
                        {
                            rep_count = 11 + ASE_ConsumeBits(&bb, 7);
                        }
                        else
                        {
                            /* Invalid len */
                            Assert(0);
                        }

                        while (rep_count--)
                        {
                            lit_len_dist_table[lit_len_count++] = rep_val;
                        }
                    }
                    Assert(lit_len_count == len_count);
                }
                else
                {
                    /* Fixed table */
                    hlit = 288;
                    hdist = 32;
                    u32 index = 0;
                    for (u32 i = 0; i < countof(ASE_huff_bl_counts); ++i)
                    {
                        u32 bit_count = ASE_huff_bl_counts[i][1];
                        u32 last_valuie = ASE_huff_bl_counts[i][0];
                        while (index <= last_valuie)
                        {
                            lit_len_dist_table[index++] = bit_count;
                        }
                    }
                }

                /* Decode */
                ASE_HuffDict lit_len_huffman = ASE_InitHuffDict(temp.arena, 15, lit_len_dist_table, hlit);
                ASE_HuffDict dist_huffman = ASE_InitHuffDict(temp.arena, 15, lit_len_dist_table + hlit, hdist);

                for (;;)
                {
                    u32 lit_len = ASE_DecodeHuffDict(&lit_len_huffman, &bb);
                    if (lit_len <= 255)
                    {
                        *dst++ = lit_len & 0xFF;
                    }
                    else if (lit_len >= 257)
                    {
                        u32 length_index = (lit_len - 257);
                        ASE_HuffEntry length_entry = ASE_huff_length_table[length_index];
                        u32 length = length_entry.symbol;
                        if (length_entry.bits_used > 0)
                        {
                            u32 extra_bits = ASE_ConsumeBits(&bb, length_entry.bits_used);
                            length += extra_bits;
                        }

                        u32 dist_index = ASE_DecodeHuffDict(&dist_huffman, &bb);
                        ASE_HuffEntry dist_entry = ASE_huff_dist_table[dist_index];
                        u32 distance = dist_entry.symbol;
                        if (dist_entry.bits_used > 0)
                        {
                            u32 extra_bits = ASE_ConsumeBits(&bb, dist_entry.bits_used);
                            distance += extra_bits;
                        }
                        u8 *src = dst - distance;
                        while (length--)
                        {
                            *dst++ = *src++;
                        }
                    }
                    else
                    {
                        break;
                    }
                }

                EndTempArena(temp);
            } break;

            case ASE_BlockType_Reserved:
            {
                /* TODO */
                Assert(0);
            } break;
        }
    }

    EndScratch(scratch);
}

////////////////////////////////
//~ Error handling

void ASE_PushError(Arena *arena, ASE_ErrorList *list, String msg_src)
{
    ASE_Error *e = PushStruct(arena, ASE_Error);
    e->msg = CopyString(arena, msg_src);
    if (!list->first)
    {
        list->first = e;
    }
    else
    {
        list->last->next = e;
    }
    list->last = e;
    ++list->count;
}

////////////////////////////////
//~ Decode image

u32 ASE_BlendMulU8(u32 a, u32 b)
{
    u32 t = (a * b) + 0x80;
    return ((t >> 8) + t) >> 8;
}

u32 ASE_Blend(u32 src, u32 dst, u8 opacity)
{
    u32 dst_r = (dst & 0xff);
    u32 dst_g = (dst >> 8) & 0xff;
    u32 dst_b = (dst >> 16) & 0xff;
    u32 dst_a = (dst >> 24) & 0xff;

    u32 src_r = (src & 0xff);
    u32 src_g = (src >> 8) & 0xff;
    u32 src_b = (src >> 16) & 0xff;
    u32 src_a = (src >> 24) & 0xff;

    src_a = (u8)ASE_BlendMulU8(src_a, opacity);
    u32 a = src_a + dst_a - ASE_BlendMulU8(src_a, dst_a);
    u32 r, g, b;
    if (a == 0)
    {
        r = g = b = 0;
    }
    else
    {
        r = dst_r + (src_r - dst_r) * src_a / a;
        g = dst_g + (src_g - dst_g) * src_a / a;
        b = dst_b + (src_b - dst_b) * src_a / a;
    }

    return r | (g << 8) | (b << 16) | (a << 24);
}

void ASE_MakeDimensionsSquareish(ASE_Header *header, u32 *frames_x, u32 *frames_y, u64 *image_width, u64 *image_height)
{
    /* Try and get image resolution into as much of a square as possible by
     * separating frames into multiple rows. */
    while (*frames_x > 1)
    {
        u64 new_frames_x = *frames_x - 1;
        u64 new_frames_y = ((header->frames - 1) / new_frames_x) + 1;
        u64 new_image_width = header->width * new_frames_x;
        u64 new_image_height = header->height * new_frames_y;
        if (new_image_width >= new_image_height)
        {
            *frames_x = new_frames_x;
            *frames_y = new_frames_y;
            *image_width = new_image_width;
            *image_height = new_image_height;
        }
        else
        {
            break;
        }
    }
}

ASE_DecodedImage ASE_DecodeImage(Arena *arena, String encoded)
{
    __prof;

    TempArena scratch = BeginScratch(arena);
    ASE_DecodedImage result = ZI;

    BB_Buff bb = BitbuffFromString(encoded);
    BB_Reader br = BB_ReaderFromBuffNoDebug(&bb);
    ASE_Header ase_header;
    BB_ReadBytes(&br, StringFromStruct(&ase_header));

    if (ase_header.magic != 0xA5E0)
    {
        ASE_PushError(arena, &result.errors, Lit("Not a valid aseprite file"));
        goto abort;
    }

    if (ase_header.color_depth != 32)
    {
        String msg = StringFormat(scratch.arena,
                                  Lit("Only 32 bit rgba color mode is supported (got %F)"),
                                  FmtUint(ase_header.color_depth));
        ASE_PushError(arena, &result.errors, msg);
        goto abort;
    }

    u64 frame_width = ase_header.width;
    u64 frame_height = ase_header.height;

    u32 frames_x = ase_header.frames;
    u32 frames_y = 1;
    u64 image_width = frame_width * frames_x;
    u64 image_height = frame_height * frames_y;
    ASE_MakeDimensionsSquareish(&ase_header, &frames_x, &frames_y, &image_width, &image_height);

    result.width = image_width;
    result.height = image_height;
    /* TODO: Optimize this. Naive memzero is bloating the decode time for large images. */
    result.pixels = PushStructs(arena, u32, image_width * image_height);

    u32 num_layers = 0;
    ASE_Layer *layer_head = 0;

    Ace_Cel *cel_head = 0;
    Ace_Cel *cel_tail = 0;

    //- Iterate frames
    u32 num_frames = 0;
    for (u16 i = 0; i < ase_header.frames; ++i)
    {
        ASE_FrameHeader frame_header;
        BB_ReadBytes(&br, StringFromStruct(&frame_header));

        u32 num_chunks = frame_header.chunks_new;
        if (num_chunks == 0)
        {
            Assert(frame_header.chunks_old != 0xFFFF);
            num_chunks = frame_header.chunks_old;
        }

        //- Iterate chunks in frame
        for (u32 j = 0; j < num_chunks; ++j)
        {
            u32 chunk_size = BB_ReadUBits(&br, 32);
            ASE_ChunkKind chunk_type = BB_ReadUBits(&br, 16);

            /* Chunk size includes size & type */
            Assert(chunk_size >= 6);
            chunk_size -= 6;

            u64 chunk_end_pos = BB_GetCurrentReaderByte(&br) + chunk_size;

            switch (chunk_type)
            {
                //- Decode layer
                case ASE_ChunkKind_Layer:
                {
                    ASE_Layer *layer = PushStruct(scratch.arena, ASE_Layer);
                    layer->next = layer_head;
                    layer_head = layer;

                    layer->flags = BB_ReadUBits(&br, 16);
                    layer->type = BB_ReadUBits(&br, 16);
                    layer->child_level = BB_ReadUBits(&br, 16);

                    /* Ignoring layer default width & height */
                    BB_SeekBytes(&br, sizeof(u16) * 2);

                    layer->blend_mode = BB_ReadUBits(&br, 16);
                    if (layer->blend_mode != 0)
                    {
                        ASE_PushError(arena,
                                            &result.errors,
                                            Lit("Layer has unsupported blend mode (only 'Normal' mode is supported). Tip: Try using 'merge down' to create a normal layer as a workaround"));
                        goto abort;
                    }

                    layer->opacity = BB_ReadUBits(&br, 8);
                    if (!(ase_header.flags & 1))
                    {
                        layer->opacity = 255;
                    }

                    BB_SeekBytes(&br, sizeof(u8) * 3);

                    u16 str_len = BB_ReadUBits(&br, 16);
                    layer->name = (String) { str_len, PushStructsNoZero(scratch.arena, u8, str_len) };
                    BB_ReadBytes(&br, layer->name);

                    if (layer->type == 2)
                    {
                        layer->tileset_index = BB_ReadUBits(&br, 32);
                    }

                    layer->index = num_layers++;
                } break;

                //- Decode cel
                case ASE_ChunkKind_Cel:
                {
                    Ace_Cel *cel = PushStruct(scratch.arena, Ace_Cel);
                    if (cel_tail)
                    {
                        cel_tail->next = cel;
                    }
                    else
                    {
                        cel_head = cel;
                    }
                    cel_tail = cel;

                    cel->layer_index = BB_ReadUBits(&br, 16);
                    cel->x_pos = BB_ReadIBits(&br, 16);
                    cel->y_pos = BB_ReadIBits(&br, 16);
                    cel->opacity = BB_ReadUBits(&br, 8);
                    cel->type = BB_ReadUBits(&br, 16);
                    cel->z_index = BB_ReadIBits(&br, 16);
                    BB_SeekBytes(&br, sizeof(u8) * 5);

                    cel->frame_index = num_frames;

                    switch (cel->type)
                    {
                        case ASE_CelKind_RawImage:
                        {
                            /* Unsupported */
                            BB_SeekToByte(&br, chunk_end_pos);
                        } break;

                        case ASE_CelKind_Linked:
                        {
                            cel->frame_pos = BB_ReadUBits(&br, 16);
                            /* Actual linking happens later after iteration */
                        } break;

                        case ASE_CelKind_CompressedImage:
                        {
                            cel->width = BB_ReadUBits(&br, 16);
                            cel->height = BB_ReadUBits(&br, 16);

                            cel->pixels = PushStructsNoZero(scratch.arena, u32, cel->width * cel->height);
                            u8 *huffman_encoded = BB_ReadBytesRaw(&br, chunk_end_pos - BB_GetCurrentReaderByte(&br));
                            if (huffman_encoded)
                            {
                                ASE_Inflate((u8 *)cel->pixels, huffman_encoded);
                            }
                        } break;

                        case ASE_CelKind_CompressedTilemap:
                        {
                            /* Unsupported */
                            ASE_PushError(arena, &result.errors, Lit("Tilemaps are not supported"));
                            goto abort;
                        } break;
                    }
                } break;

                default:
                {
                    BB_SeekToByte(&br, chunk_end_pos);
                } break;
            }
        }
        ++num_frames;
    }

    //- Create ordered layers array
    ASE_Layer **layers_ordered = PushStructsNoZero(scratch.arena, ASE_Layer *, num_layers);
    for (ASE_Layer *layer = layer_head; layer; layer = layer->next)
    {
        layers_ordered[layer->index] = layer;
    }

    //- Link cels
    Ace_Cel **cels_ordered = PushStructsNoZero(scratch.arena, Ace_Cel *, num_frames * num_layers);
    for (Ace_Cel *cel = cel_head; cel; cel = cel->next)
    {
        cels_ordered[(cel->frame_index * num_layers) + cel->layer_index] = cel;
        if (cel->type == ASE_CelKind_Linked)
        {
            Ace_Cel *ref_cel = cels_ordered[(cel->frame_pos * num_layers) + cel->layer_index];
            cel->width = ref_cel->width;
            cel->height = ref_cel->height;
            cel->pixels = ref_cel->pixels;
        }
    }

    //- Assemble image from cels
    {
        __profn("Build image from cels");
        for (Ace_Cel *cel = cel_head; cel; cel = cel->next)
        {
            ASE_Layer *layer = layers_ordered[cel->layer_index];
            /* Only draw visible layers */
            if (layer->flags & 1)
            {
                u8 opacity = (cel->opacity / 255.0f) * (layer->opacity / 255.0f) * 255.0f;

                i32 cel_width = cel->width;
                i32 cel_height = cel->height;

                i32 cel_left = 0;
                i32 cel_right = cel_width;
                i32 cel_top = 0;
                i32 cel_bottom = cel_height;

                i32 frame_left = cel->x_pos;
                i32 frame_top = cel->y_pos;

                i32 image_left = frame_left + ((cel->frame_index % frames_x) * frame_width);
                i32 image_top = frame_top + ((cel->frame_index / frames_x) * frame_height);

                /* Adjust bounds to ensure pixels outside of frame boundaries
                 * aren't (aseprite keeps chunks outside of frame around in
                 * project file). */
                {
                    i32 frame_right = cel_width + frame_left;
                    i32 frame_bottom = frame_top + cel_height;
                    if (frame_left < 0)
                    {
                        cel_left += -frame_left;
                        frame_left = 0;
                    }
                    if (frame_top < 0)
                    {
                        cel_top += -frame_top;
                        frame_top = 0;
                    }
                    if (frame_right > (i32)frame_width)
                    {
                        cel_right -= (frame_right - frame_width);
                        frame_right = frame_width;
                    }
                    if (frame_bottom > (i32)frame_height)
                    {
                        cel_bottom -= (frame_bottom - frame_height);
                        frame_bottom = frame_height;
                    }
                }

                for (i32 cel_y = cel_top; cel_y < cel_bottom; ++cel_y)
                {
                    i32 image_y = image_top + cel_y;
                    i32 cel_stride = cel_y * cel_width;
                    i32 image_stride = image_y * image_width;
                    for (i32 cel_x = cel_left; cel_x < cel_right; ++cel_x)
                    {
                        i32 image_x = image_left + cel_x;
                        u32 cel_pixel = cel->pixels[cel_x + cel_stride];
                        u32 *image_pixel = &result.pixels[image_x + image_stride];
                        *image_pixel = ASE_Blend(cel_pixel, *image_pixel, opacity);
                    }
                }
            }
        }
    }

    /* Assert all data was read */
    Assert(BB_NumBytesRemaining(&br) == 0);

abort:

    if (result.errors.count <= 0)
    {
        result.success = 1;
    }

    EndScratch(scratch);
    return result;
}

////////////////////////////////
//~ Decode sheet

ASE_DecodedSheet ASE_DecodeSheet(Arena *arena, String encoded)
{
    __prof;

    ASE_DecodedSheet result = ZI;

    BB_Buff bb = BitbuffFromString(encoded);
    BB_Reader br = BB_ReaderFromBuffNoDebug(&bb);
    ASE_Header ase_header;
    BB_ReadBytes(&br, StringFromStruct(&ase_header));

    u64 frame_width = ase_header.width;
    u64 frame_height = ase_header.height;

    u32 frames_x = ase_header.frames;
    u32 frames_y = 1;
    u64 image_width = frame_width * frames_x;
    u64 image_height = frame_height * frames_y;
    ASE_MakeDimensionsSquareish(&ase_header, &frames_x, &frames_y, &image_width, &image_height);

    u32 num_frames = 0;
    ASE_Frame *frame_head = 0;

    u32 num_spans = 0;
    ASE_Span *span_head = 0;

    u32 num_slice_keys = 0;
    ASE_SliceKey *slice_key_head = 0;

    //- Iterate frames
    for (u16 i = 0; i < ase_header.frames; ++i)
    {
        ASE_FrameHeader frame_header;
        BB_ReadBytes(&br, StringFromStruct(&frame_header));

        u32 num_chunks = frame_header.chunks_new;
        if (num_chunks == 0)
        {
            Assert(frame_header.chunks_old != 0xFFFF);
            num_chunks = frame_header.chunks_old;
        }

        ASE_Frame *frame = PushStruct(arena, ASE_Frame);
        frame->next = frame_head;
        frame_head = frame;

        frame->index = i;
        frame->duration = frame_header.frame_duration_ms / 1000.0;

        u32 frame_tile_x = i % frames_x;
        u32 frame_tile_y = i / frames_x;

        u32 frame_x1 = frame_tile_x * frame_width;
        u32 frame_y1 = frame_tile_y * frame_height;
        u32 frame_x2 = frame_x1 + frame_width;
        u32 frame_y2 = frame_y1 + frame_height;
        frame->x1 = frame_x1;
        frame->y1 = frame_y1;
        frame->x2 = frame_x2;
        frame->y2 = frame_y2;

        frame->index = i;
        frame->duration = frame_header.frame_duration_ms / 1000.0;

        //- Iterate chunks in frame
        for (u32 j = 0; j < num_chunks; ++j)
        {
            u32 chunk_size = BB_ReadUBits(&br, 32);
            ASE_ChunkKind chunk_type = BB_ReadUBits(&br, 16);

            /* Chunk size includes size & type */
            Assert(chunk_size >= 6);
            chunk_size -= 6;

            u64 chunk_end_pos = BB_GetCurrentReaderByte(&br) + chunk_size;

            switch (chunk_type)
            {
                //- Decode tags
                case ASE_ChunkKind_Tags:
                {
                    u16 frame_span_count = BB_ReadUBits(&br, 16);
                    BB_SeekBytes(&br, 8);

                    for (u16 k = 0; k < frame_span_count; ++k)
                    {
                        ASE_Span *span = PushStruct(arena, ASE_Span);
                        span->next = span_head;
                        span_head = span;

                        span->start = BB_ReadUBits(&br, 16);
                        span->end = BB_ReadUBits(&br, 16);
                        BB_SeekBytes(&br, 13);

                        u16 str_len = BB_ReadUBits(&br, 16);
                        span->name = (String) { str_len, PushStructsNoZero(arena, u8, str_len) };
                        BB_ReadBytes(&br, span->name);

                        ++num_spans;
                    }

                } break;

                //- Decode slice
                case ASE_ChunkKind_Slice:
                {
                    ASE_SliceKey *slice_key = PushStruct(arena, ASE_SliceKey);
                    slice_key->next = slice_key_head;
                    slice_key_head = slice_key;

                    u32 num_slices = BB_ReadUBits(&br, 32);
                    slice_key->num_slices = num_slices;

                    u32 flags = BB_ReadUBits(&br, 32);
                    BB_SeekBytes(&br, 4);

                    u16 str_len = BB_ReadUBits(&br, 16);
                    slice_key->name = (String) { str_len, PushStructsNoZero(arena, u8, str_len) };
                    BB_ReadBytes(&br, slice_key->name);

                    for (u32 k = 0; k < num_slices; ++k)
                    {
                        ASE_Slice *slice = PushStruct(arena, ASE_Slice);
                        slice->next = slice_key->slice_head;
                        slice_key->slice_head = slice;

                        u32 start = BB_ReadUBits(&br, 32);
                        i32 x = BB_ReadIBits(&br, 32);
                        i32 y = BB_ReadIBits(&br, 32);
                        u32 width = BB_ReadUBits(&br, 32);
                        u32 height = BB_ReadUBits(&br, 32);
                        if (flags & 0x01)
                        {
                            /* Skip 9-patches info */
                            BB_SeekBytes(&br, 128);
                        }
                        if (flags & 0x02)
                        {
                            /* Skip pivot info */
                            BB_SeekBytes(&br, 64);
                        }

                        slice->start = start;
                        slice->x1 = x;
                        slice->y1 = y;
                        slice->x2 = x + width;
                        slice->y2 = y + height;
                    }

                    ++num_slice_keys;
                } break;

                /* TODO */
                //case ASE_ChunkKind_Userdata

                default:
                {
                    BB_SeekToByte(&br, chunk_end_pos);
                } break;
            }
        }
        ++num_frames;
    }

    /* Assert all data was read */
    Assert(BB_NumBytesRemaining(&br) == 0);

    result.image_size = VEC2(image_width, image_height);
    result.frame_size = VEC2(frame_width, frame_height);
    result.num_frames = num_frames;
    result.num_spans = num_spans;
    result.num_slice_keys = num_slice_keys;
    result.frame_head = frame_head;
    result.span_head = span_head;
    result.slice_key_head = slice_key_head;

    if (result.errors.count <= 0)
    {
        result.success = 1;
    }

    return result;
}